> so, naturally, along with the language validation suite> (if there is one), one of the first big tests of your new compiler is> whether it can compile itself.

The other point it is possible to bootstrap the thing. Once you have a
minimal compiler it can be used to compile the full version. It is also
easier to add additional features. Delphi distributions for example
includes the complete source code of the compiler and the components.

A different example is Forth. While you can write Forth systems in
another language such as C a large proportion of them have a minimum
word set in machine code and the rest is written in Forth.